Offset image transfer process



March 11, 1969 R. H. BECK OFFSET IMAGE TRANSFER PROCESS Filed July 28,1966 Sheet of4 INVENTOR ROBERT HAUN BECK ATTORNEY March 11, 1969 R. H.BECK 3,431,846

OFFSET IMAGE TRANSFER PROCESS Filed Ju1y28. 1966 Sheet 2 of 4 Fl 6. a ,5

INVENTOR ROBERT HAUN BECK ATTORNEY Marchll, 1969 R. H. BECK OFFSET IMAGETRANSFER PROCESS Sheet Filed July 28, 1966 ROBERT HAUN BECK ATTORNEYMarch 11, 1969 BECK OFFSET IMAGE TRANSFER PROCESS Fild July 28. 1966FIG. 6

Sheet hVACUUM PUMP \J hwwuuu PUMP 9 VARIABLE SPEED W MOTOR CLUTCH COIL II l ROBERT HAUN BECK United States Patent 3,431,846 OFFSET IMAGETRANSFER PROCESS Robert Haun Beck, Fair Haven, N..I., assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware Filed July 28, 1966, Ser. No. 568,663

US. Cl. 101426 Int. Cl. B410 3/00; B41f 3/12; B41m 1/06 ABSTRACT OF THEDISCLOSURE An offset image transfer process and apparatus comprising aframe, two coating rolls carried by the frame, one roll being one-halfthe diameter of the other, means for rotating the rolls in synchronismand in surface contact, and for disengaging the surfaces; and securingmeans on the larger roll to hold a matrix image-bearing sheet and animage receptor sheet 180 apart while in a fixed position on the largerroll. This process is useful in color proofing where images in variouscolors are transferred in superimposed registrations onto a receptorsheet.

This invention relates to an offset printing machine and moreparticularly to dry offset image transfer for color proofing from shearsensitive photopolymer coatings.

The offset method of ink transfer from a planographic printing plate topaper is old. The offset method of transfer is used in machines whichare now commercially available, for example, A. B. Dick Model 320duplicator. Generally in these machines more than 2 rolls are needed andfountain solutions are necessary. The transfer is done wet while onlyone pass completes the transfer. Since only one pass is needed noprecise method of hold down or registration of matrix and receptor isneeded or available. In a typical offset printing press there exists endplay in the rolls and backlash between the gears coupling the rolls.Furthermore, the prior art equipment is not economically useful in colorproofing such as for four color half-tone transfer. This results becauseseparation halftones are proofed by first making an offset test plateand then making short runs under actual printing conditions.

The offset image transfer machine of this invention is designed toprovide a novel apparatus to make color proofing copies with a minimumof time, effort and cost while eliminating the need of a wet system.This apparatus comprises two cylindrical rolls of different diameters,the largest being twice the diameter of the other; drive means to rotatethe rolls; synchronizing means causing the smaller roll to rotate twiceper rotation of said larger roll; actuating means to engage anddisengage the surface of the rolls with each other; and securing meanson the larger roll to hold a matrix and image receptor on the roll in afixed position.

A practical offset dry image transfer machine of this invention will nowbe described with reference to the following drawings.

FIGURE 1 is an isometric view of the assembled machine.

FIGURE 2 is a front view of the essential parts of the machine.

FIGURE 3 is an end view showing the relationship of the rolls to eachother and to the drive motor.

FIGURE 4 is a sectional view of the engage-disengage pivot mechanismtaken from See. 4-4 of FIGURE 2.

FIGURE 5 is a view of the system which moves the engage-disengage pivotarm in the transverse direction.

FIGURE 6 is a schematic view showing the electrical circuits and certainparts of the system controlling the machine.

FIGURE 7 is an isometric view of the proofing cylinder and a schematicview of the vacuum hold-down system.

2 Claims 3,431,846 Patented Mar. 11, 1969 FIGURE 8 shows the shaftmountings at one end with the position of the preloaded ball bearingsand the drag brake.

Referring now to the drawings wherein similar parts have similarreference numerals throughout the several figures, the machines of thisinvention may have a suitable base frame 1, pressed metal casing 2 and acontrol box 3.

With particular reference to FIGURES l and 2 a proofing cylinder roll 4is journalled in bearing supports 5 and carried by the base frame. Onthe outer surface of the proofing cylinder are imbedded registrationpins 6 to accommodate the matrix and receptor papers as they are to bepositioned out of phase on cylinder 4. Vacuum for paper hold-down isapplied through two sets of open air channels 7 set in the proofingcylinder 4 (only one set shown). The channels are separated so thatvacuum holddown for matrix and receptor paper may be separatelycontrolled.

Immediately behind the proofing cylinder is the offset transfer cylinderroll 8. In size the offset transfer cylinder is one half the diameter ofthe proofing cylinder. It is mounted on an eccentric shaft andjournalled into suitable bearing supports carried by the base frame. Inspace relationship, it is mounted on an eccentric shaft to that in thedisengaged position the center of a cross section of the offset rolllies below a line connecting the centers of the two rolls in the engagedposition, see FIGURE 3. The center of the offset transfer cylinder 8 inthe engaged position is marked by numeral 50, and in the disengagedposition by numeral 51. Rotation of the offset cylinder from thedisengage to the engage position, that is from reference center point 51to reference center point 50, is a clockwise rotation as viewed inFIGURE .3. The outer surface of the offset cylinder 8 is covered by astandard offset printing blanket consisting of rubber facing on a rubberimpregnated fabric base.

An electric motor 9 is attached to the shaft of the proofing cylinderthrough a pulley arrangement 10. In turn, the drive system of theproofing cylinder 4 is geared to the offset cylinder on a 1 to 2 ratiothrough gear box 11.

The proofing cylinder is mounted on a fixed center while the offsetcylinder may assume either of two positionsengage with the proofingcylinder or disengage from the proofing cylinder. The engage-disengagesystem works as follows. (See FIGURES 4 and 5.) Axially mounted on theproofing cylinder shaft is the engage cam 12 and the disengage cam 13.Axially mounted on the offset cylinder shaft is pivot arm 14. Attachedto the upper end of pivot arm 14 is the cam follower 15 which whenengaged with cam 13 causes the top of the pivot arm 14 to rock forwarddisengaging the offset cylinder 8 from the proofing cylinder 4. When camfollower 16 is caused to engage cam 12, the top of the pivot arm rocksbackward engaging the rolls.

The cams 12 and 13 utilized in the preferred apparatus as hereindescribed have part of their internal section removed so that each camresembles a container such as a round pan. The internal diametercontains the actual cam riser 54 (shown only for cam 12) surface. Thecam followers 15 and 16' are arranged to extend into the interior of thecams when transversely moved and thereby contact the cam riser. The camrisers merely act to trip the cam followers to begin or end a printingcycle. Once tripped, the cam followers are locked into place just out ofreach of the cam risers by the action of holding magnets 36 or 37. Asthe drums rotate during a printing cycle there is no action between thecam followers and cam risers.

Shaft 17 upon which the offset cylinder 8 and pivot arm 14- are mountedis eccentrically constructed and 0perates in a manner similar to a crankshaft in that the rotational effect caused by the rocking of the pivotarm 14 will cause the offset cylinder to engage and disengage.

In order that pivot arm 14 may cause cam followers 15 or 16 to engageone cam or the other, the pivot arm is made to slide along shaft 17 bythe sliding mechanism 18 which is positioned by a mechanical yoke 19 andcontrolled by solenoids 20 and 21. Solenoid 20 positions the camfollower 15 to ride on cam 13 and disengage the offset cylinder, whilesolenoid 21 causes cam follower 16 to ride on cam 12 and engage theoifset cylinder. The sliding mechanism 18 is keyed to the shaft by asliding key 48.

End play or transverse motion of the drums is eliminated by the use ofholding means such as preloaded ball bearings commercially obtainable,i.e., New Departure Ball Bearing Type 20,000, shown in FIGURE 8 andlabelled numeral 40. The bearings which have an angular contact designare loaded by adjusting means 41, a hearing locknut with a complementingbearing lock washer 42.

Backlash between the teeth of gear system 11 is contained by the use ofa spring loaded friction disc engaged as a drag brake. This drag brakeis also commercially obtainable. Referring to FIGURE 8, the brakingmeans is located on shaft 17 adjacent cylinder 8 and is composed of afriction disc 43, a retaining ring 44, a spring washer 45 and acompression adjusting nut 46. The compression adjusting nut 46, thespring washer 45 and the retaining ring 44 are stationary parts. Byturning compression adjusting nut 46, the drag created by friction disc43 can be controlled to prevent backlash between the proofing cylinder 4and the offset transfer cylinder 8.

The vacuum used for locking the matrix and receptor paper on theprinting cylinder is created by pumps 22 and 23, see FIGURE 7. A vacuumis supplied to the surface of the proofing cylinder in the followingmanner. The outer surface of the proofing cylinder contains two sets ofopen air channels 7. These channels are in operative contact with vacuumports 38 and 39. One system of interconnected channels leads into vacuumport 38 and vacuum port 38 is connected by tubing to rotary joint 27 andcontinues on to vacuum pump 23. This system services the matrix side ofthe proofing cylinder. Vacuum port 39 with its related channel system isconnected to rotary joint 26 and vacuum is supplied through pump 22.This system services the receptor side of the proofing cylinder. Gages24 and 25 are vacuum gages mounted in the control box 3. Rotary joints26 and 27 are mounted on the ends of the proofing cylinder shaft.

The preparations necessary prior to machine opera tion are as follows.The matrix coated with a polymerizable photosensitive layer is shearsensitive in the unexposed areas. Such element is described in a patentapplication by Chambers, entitled Polymerization Processes and ElementsTherefor filed July 7, 1966, Ser. No. 6 8,- 367. Exposure of the matrixis through the back of the positive which produces a right reading imageon the matrix. After exposure to a half-tone positive under ultravioletlight, the cover sheet is carefully stripped off and the matrix ismounted in register on the proofing cylinder. The paper receptor is alsomounted on the proofing cylinder 180 away from the matrix. Vacuum pumps23 and 24 are turned on by manual switches 50 and 51 to assist in holddown. Following this, the machine is ready for operation.

Looking to FIGURE 6 will aid in defining the machine step sequence. Themotor controller is an S47 Silicon Controller Rectifier made by GeraldK. Heller Co., of Las Vegas, Nev.

Motor '9 is energized by manual switch 52. Through pulley system 10, therolls 4 and 8 begin to rotate. The gears coupling the two rolls arealways engaged; there- Lfore, synchronized rotation begins when motor 9is turned on. Variable speed potentiometer 28 is used to adjusting themotor speed until the proofing cylinder 4 is rotating at the desiredrpm.

Single pole, momentary contact push button 29 is depressed and held. Toprevent a collision of parts, i.e., to keep cam follower 16 in itstransverse motion from landing on the side of cam riser 54, the clutch30 will not be activated until counting switch 31 is activated by itscamming surface 47, indicating the mechanical parts are in a compatiblespace relationship to engage each other. With push button 29 depressedand counting switch 31 activated, power is fed through the clutch coil30 into the offset roll-engage solenoid '21. Contact 53 closescompleting the power circuit. At the same time, contact 35 closes tomaintain a completed circuit to service the clutch coil when push button29 is released, while contact 32 opens keeping solenoid 20 from beingactivated.

Contacts 32, 35 and '53 are all contained in one component and are in afixed relationship to each other. That is 32 is normally closed while 35and 53 are open. Conversely when 32 is open 35 and 53 are closed.

Mechanically, looking to FIGURES 4 and 5, once the offset roll-engagesolenoid 21 is activated, it pulls the mechanical yoke 19 causing thetransverse sliding mechanism 18 to move pivot arm 14 towards cam 12where cam follower 16 will engage cam 12. Once the follower 16 hits theraised portion of cam 12, this will cause the top of pivot arm 14 torock back moving the bottom of pivot arm 14 to engage switch 33 whichactivates the counter 34. After the initial pivot arm action resultingfrom cam 12, the arm 14 is held in the engaged position by magnetic stop36 for the duration of the printing cycle. In like manner, magnetic stop37 will hold pivot arm 14 in the disengaged position.

When counter 34 counts out its preset number of revolutions, itde-energizes the clutch coil 30 by opening contact 35, and goes on tode-energize solenoid 21 by opening contact 53 while contact 32 closes.Switch 49 is closed when not engaged by arm 14 and contact 32 is opened.When contact 32 closes a power circuit is completed through solenoid 20which is now activated and acts to shift the slide mechanism causing therocker arm 14 to disengage the rolls. To prevent solenoid 20 fromburning out, switch 49 will open by the action of arm 14 after contact32 is closed and solenoid 20 has pulled the rocker arm 14 back to thedisengaged position. The pivot arm 14 will be held in this disengagedposition by magnetic stop 37.

As the disengage solenoid 20 is activated, it pulls the mechanical yoke19 towards it which causes the transverse slide mechanism 18 to movepivot arm 14 towards cam 13 where cam follower 15 will engage cam wheel13. This will cause the top of pivot arm 14 to rock forward and thebottom backwards so that the bottom engages micro switch 49 opening thisswitch and de-energizing solenoid 20. The offset roller is disengagedfrom the printing roll due to this rotation of the pivot arm and theprinting cycle is completed.

Transfer of the image occurs by the matrix mounted on the printing drumleaving an image on the offset roll and this image is then transferredback to the printing drum but onto the receptor paper which is exactlyopposite the matrix. This is accomplished by the fact that the printingcylinder is twice as large as the offset roll in diameter and the offsetcylinder is geared to the proofing cylinder on a 2 to 1 ratio.

When the two rolls engage, the printing roll, being made of a hardermaterial than the offset roll, causes the offset roll to be depressed.When the matrix appears in this depressed area, shear forces are set upand these shear forces cause the unexposed and therefore theunpolymerized image areas of the matrix to become fluid due to thepseudoplastic nature of the coating and transfer from the matrix to theoffset cylinder occurs. Thin layers of image are transferred first fromthe matrix on the printing cylinder to the rubber blanket of the offsetroll and then to the receptor paper on the printing cylinder with eachrevolution. Multiple revolutions are generally necessary for colortransfer of the same image, therefore the need for proper registration.In addition, when four color half-tone positives are to be proofed, eachcolor is transferred separately to the same receptor and proper matrixregistration is essential. For example, a yellow matrix may be usedfirst and take 15 revolutions for proper transfer. The yellow matrix isthen removed by first turning the vacuum to the matrix side of the rolloff, removing the yellow matrix and replacing it with a cyan matrix, forexample. The cyan matrix would be placed in registration, vacuum appliedand the machine run for the desired number of revolutions. This is thenrepeated for any other color to be transferred. Since the transfer is byoffset, the right reading matrix image transfers first to the offsetcylinder as a wrong reading image then to the receptor paper as a rightreading image.

The machine described above can be modified in various ways, forexample, the rolls can be activated by one or more motors linked to thedifferent rolls by means of gears, belts or chains and provided with asuitable clutch. The various parts of the machine can be made fromconventional materials of construction. The frame and covers can be madeof metal such as steel, steel alloys, aluminum, aluminum alloys, copper,brass, etc. or even plastic materials. They may be painted or coveredwith protective surfaces. The design of the rolls may be modified insize so long as the matrix, transfer image, and receptor paper are keptin phase to effectuate transfer from matrix to receptor.

The machines of this invention are useful for transferring a nearly dryto the touch image from a matrix coated basically with a polymerizablemonomer and a thixotropic agent as described in the above-identifiedChambers application Ser. No. 563,367.

The matrices of the Chambers application comprise a support, usually aflexible sheet, having coated thereon a photopolymerziable stratum, saidphotopolymerizable stratum comprising a uniform admixture of (a) aninorganic thixotropic binder (b) a non-gaseous ethylenically unsaturatedcompound containing at least one terminal ethylenic group and beingcapable of forming a high polymer by free radical initiated chainpropagating, addition polymerization, and having a plasticizing actionon (a).

Constituents (a) and (b) being present in from 0.2 to 12 parts by weightand 1 to 30 parts by weight, respectively.

Generally, the photopolymerizable composition is coated from adispersion in 38 to 90 parts by weight of water, alcohol, or mixturesthereof. The photopolymerizable coating composition preferably contains4 to 5 parts by weight of constituent (a) and from 1.4 to 1.9 parts byweight of constituent (b). Preferably the photopolymerizablecompositions also contain a free radical generating additionpolymerization initiator in amounts ranging from 0.05 to 2 parts byweight. A pigment and pigment dispersant may be added and are generallypresent in 0.4 to 25 and 0.05 to 2 parts by weight, respectively. Also,small amounts of thermoplastic organic polymers as described in Plambeck2,760,863 may be present as diluents in amounts up to 5% of thethixotropic binder.

Preferred thixotropic agents that range in size from 5 to 500millimicrons are boehmite alumina crystals having a length to diameterratio of 20:1, clay mixtures of silicate oxides, e.g., bentonites andgels containing 99.5% SiO with 0.5% of mixed metallic oxides having asurface area of 250-350 square meters/ g.

A preferred unsaturated compound is the triacrylate ester of thereaction product of trimethylol propane and ethylene oxide. This andother unsaturated compounds, photopolymerization initiators and othercomponents are listed in the Chambers application and the referenceslisted in said application.

Some advantages of the machine are as follows. No particular skill isrequired to operate the machine. It is self-contained, dependable anddurable. A nearly dry to the touch image is transferred which would notbe obtained by standard offset printing. The machine is comprised ofonly two rolls which eleminates the extra gear means between the threerolls of the standard offset printing press. Vacuum hold-down isprovided which is mechanically difficult in a conventional offset press.The machine is suitable for making single color transfers in addition tomultiple color transfer. The image being transferred by a multiplicityof revolutions allows one to control density.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows.

1. A process for printing an image of essentially drypressure-transferable material by offset printing which comprises (a)fastening (1) a printing member having printing areas comprising aradiation-sensitive addition polymerizable monomer and a thixotropicagent and coplanar complementary hardened areas embodying a polymer ofsaid monomer, and said thixotropic agent, and (2) a receptor sheet onopposite segments of the same printing roller; rotating in surfacecontact and in synchronism (i) said printing member and roller and (ii)an offset roller that is one-half the diameter of the printing roller sothat the offset roller rotates at twice the speed of the printingroller; and

(c) containing the rotation of said rollers a plurality of times for theprinting of each image, portions of monomer and thixotropic agent in theprinting areas being successively transferred on each rotation from theprinting member, first to the offset roller, thence to the receptorsheet to form a printed image of the desired density of monomer andthixotropic agent by plural transfers to the same receptor sheet.

2. A process as defined in claim 1, where said printing material is oneof at least two different colored materials of the same subject andafter image transfer from said material, it is removed and a secondmaterial of the same subject but of different color is locked inregister and the image of said second material is transferred to saidreceptor.

References Cited UNITED STATES PATENTS 958,484 5/1910 Evans et al.101137 2,060,082 11/1936 Johnson et al. 101382. XR 2,280,799 12/1945Davidson 10l-217 2,417,496 3/1947 Huebner 101-382 XR 2,427,904 9/1947Davidson 101217 2,759,416 8/1956 George et al 101-217 2,937,593 5/1960Ritzerfeld et al. l014l5.1 2,909,117 10/1959 Crissy 101-137 EDGAR S.BURR, Primary Examiner.

US. 01. X.R. 101 45o, 137

